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Analysis of tool-sided surface modifications for dry deep drawing of deep drawing steel and aluminum alloys in a model process
Get PDFThe concept of sustainability motivates the development of energy-saving and low-polluting production processes. A sheet metal forming process without usage of lubricants is considered as one of these green production technologies. Forming processes without the need for traditional lubricants save process steps and additional costs to remove the remaining lubrication from the workpiece after forming. In order to realize such a dry forming process and to adjust the material flow effectively, tool surfaces were modified by amorphous carbon coatings and different surface finishing processes for roughness adjustment. To verify the general feasibility of the lubricant-free metal forming process, deep drawing of rectangular cups with and without lubrication with conventional forming tools was investigated. The dry deep drawing process was modelled numerically to analyze process parameters and identify critical contact conditions. By strip drawing tests, the tribological behavior of ta-C and a-C:H coated tools with different surface treatments was investigated. The deposition process and resulting properties of a-C:H coatings were further analyzed to improve their tribological performance. The effects of the process parameters - deposition temperature and bias voltage in the deposition chamber - were investigated using the one-factor-at-a-time method. The strip drawing tests revealed a high influence of the surface roughness of coated tools on the tribological behavior. Therefore, laser based smoothing was further investigated in this study. Laser radiation at 355 nm wavelength was applied as an effective and minimum heatgenerating technique to remove the roughness asperities on ta-C coatings which are built during its growth. Finally, ta-C and a-C:H coatings were applied on tool surfaces and tested in a drawing process of strip profiles. As reference the same forming process with a conventional forming tool was carried out
Modelling coral reefs to support their local Management : A case study in the Spermonde Archipelago, Indonesia
Get PDFThe potential of simulation models to provide insights on ecological questions that are crucial for the management of marine resources has become more relevant in light of the apparent demise of coral reefs. Multiple coral reef stressors can interact in nonlinear ways, confounding ecological interpretation through field studies alone. Theoretical computer modelling offers a platform to test ecological hypotheses about multiple stressors and their systemic impacts. The main purpose of this thesis was to use coral reef ecological theory to create a model as a basis for a scientifically sound, user-friendly decision support tool for the local management of coral reefs. Four major objectives were established: (1) develop a local coral reef model representing the impacts of simultaneous stressors on key ecological groups, (2) turn it into a user-friendly decision-support tool to explore different management options, (3) collect qualitative and quantitative information on the artisanal fishery of Spermonde (Indonesia) to help understand its social drivers, and (4) apply the model to real case scenarios to project the trajectory of selected coral reef response variables. Chapter two contains the description of SEAMANCORE (Spatially Explicit simulation model for Assisting the local MANagement of COral REefs) and its development. The model has two distinct compartments, benthos and fish, which run at different spatiotemporal scales and are affected by each other and by the three modelled stressors: fishing, bleaching and nutrients. Chapter three outlines an assessment of the coral reef fishery in Spermonde, focusing on the role of the patron-client system in the fishing behaviour of individual fishermen. This study contributes to the body of scientific literature on social drivers influencing fishing behaviour by empirically showing catch and behavioural differences between fishermen within the patron-client system and independent fishermen. Quantitative data on catches obtained in this study were used to parameterize fishing scenarios in Spermonde for a real case application of the model. Chapter four stems from the previous studies and adds ecological field collected data to parameterize SEAMANCORE. First, basic scenarios of nutrients and fishery were run under standardized conditions to appraise the stressorsa effects on the modelled response variables. Fishery scenarios included a fishery ban, subsistence fishery, commercial fishery, and commercial combined with destructive fishing practices. In the second part, ten-year simulations were run for four sites in Spermonde (Indonesia) exposed to varying degrees of human impacts and different initial conditions to project their local coral reefa s trajectories. Chapter 5 summarizes the contributions of this dissertation, highlighting the limitations of the modelling approach, and provides recommendations on research directions for modelling local coral reefs and management of their associated artisanal fisheries
Lernen im Kontext : Digitale Medien für Menschen mit Lernschwierigkeiten Entwicklung und Erprobung eines mobilen Assistenzsystems für kontextbezogenes Lernen
Get PDFA model of an assistance-system was built in an intensive and multilayered process of participatory software development in the context of a sheltered-workshop for disabled people. The solution is assisting people with learning disabilities to accomplish auton-omously their job tasks. Based on emotion-recognition and specific personalized profiles the system can recognize the cognitive abilities in a certain situation and assist to coop with problems by personalized feedback. Therefor the successful completion of a task is supported and the system can prevent failures and dangerous mistakes. As a result the experience of personal confidence and self-efficacy can be fostered. By a prototype the model could be evaluated and refined. The system consists of an authoring-area for designing personalized audio-visual work instructions and a mobile assistance area, that could easily be integrated in a production station. Because of the special needs of the target group and their vulnerability a adapted version of participatory software de-velopment process has to be initiated and applied
Der Internationale Frauentag nach der Dekonstruktion von Geschlecht : eine empirisch-qualitative Vergleichsstudie zu Bündnispolitiken im Rahmen des 8. März in Berlin und in Istanbul.
Get PDFThis doctoral dissertation project aims to compare the (im-)possibility of building coalitions between political actors of diverse women's and gender-based scenes and movements in Berlin and in Istanbul with an empirical-qualitative approach. International Women's Day (IWD) was chosen as an object of research because it involves thorough discussions on women's movement(s) and feminism, as well as sex and gender. The controversial assessment of IWD paved the way for field research in Berlin (2012) and in Istanbul (2013). Data was collected by means of documents, participant observation during the preparation for and celebration of IWD, and 40 interviews with experts from civil society organizations and political institutions. The empirical data were analyzed with an approach based on Meuser and Nagel's adaptation of Grounded Theory. Due to globalization and transnationalization processes, neoliberal restructuring and debates on identity politics, researchers focusing on women and gender have observed a crisis in feminist movements, especially in the 'Western' societies since the 1990s. The strength of aimed comparison lies in the fact that in today's Turkey - unlike Germany - women's movements work towards common goals and criticize publicly. Based on a 'deep description' of IWD - while focusing on coalition building in the context of the event - the following research question ought to be answered: After the unifying collective subject of 'we women' has been decentered and deconstructed in the context of (post)structuralist, postcolonial and queerfeminist scientific discourses, how can the categories of sex and gender still function as a focal point for social movements? Thus, this dissertation deals with coalition politics among diverse women on the occasion of this transnational event
Erfolgsfaktoren im Omni-Channel-Retailing: Eine empirische Analyse der größten Unternehmen im Einzelhandel
Get PDFControlling for unobserved confounders in observational studies using large health care databases by means of instrumental variables in time-to-event analysis
Get PDFRandomized controlled trials cannot provide all necessary information about drug reactions as they are limited by several factors. Observational studies in free-living populations are therefore necessary. Large health care databases are frequently used for this purpose. A common problem of analyses based on these databases is that confounding variables are often not recorded, so that effects are inconsistently estimated. Under certain conditions instrumental variables can eliminate confounding bias, so that IV estimators can consistently estimate treatment effects. Instrumental variable methods are well established for continuous outcomes using linear regression models, where two-stage least squares are typically used. However, in time-to-event analysis no such common instrumental variable method exists. Even if the proportional hazards model is used, two-stage estimators to account for instrumental variables are only justified for rare events. The aim of this thesis is therefore to explore two-stage instrumental variable estimation for time-to-event outcomes in large health care databases if the assumption of rare events does not hold true
Bedeutung von SWEET-Genen für den pflanzlichen Zuckerexport in einer Ektomykorrhizasymbiose
Get PDFIn mutualsitic interactions between fungi and plants, such as ectomycorrhiza, the fungus contributes nutrition and obtains plant derived carbohydrates as a response. The carbohydrate transport in ectomycorrhized roots is not yet fully understood and requires additional investigations. However prerequisites for such analysis are transgenic plants. Poplar is a well established model for investigation of ectomycorrhizal symbiosis. As the generation of transgenic poplar plants is a highly time consuming process and can take up to one year a new A. rhizogenes- based transformation protocol was developed in the present thesis. Furthermore, the role of the recently discovered SWEET-proteins in the carbohydrate transport in ectomycorrhiza was investigated. Ectomycorrhiza regulated SWEET proteins were localized in the plasma membrane of Nicotiana benthamiana leaves determining their role in the carbohydrate supply of the fungal partner in ectomycorrhiza. Additionally a promoter analysis of one of the mycorrhiza-induced SWEET genes, PtSWEET 1.c, was performed and two regulatory regions could be identified. However, an ectomycorrhiza specific regulation of the promoter reporter constructs was not observed
Palynological investigation of Holocene climatic and oceanic variability in South Africa and the southern Benguela upwelling system
Get PDFSouth Africa is very sensitive to climate change, because it is located between two atmospheric systems (subtropical and warm-temperate systems) and two oceanic systems (Benguela Current and Agulhas Current). Presently, the seasonal changes of atmospheric and oceanic systems induce a pronounced rainfall seasonality comprised of three different rainfall zones (summer rainfall zone, SRZ; year-round rainfall zone, YRZ and winter rainfall zone, WRZ) over South Africa. However, the seasonality development during the Holocene in South Africa is poorly understood and the driving forces of the climate change are debated. Therefore, this study aims to provide a detailed reconstruction of Holocene climate and vegetation variability of South Africa, palaeoceanographic changes in the southern Benguela upwelling system as well as the land-ocean linkages. In the first part of this thesis, the spatial distribution of pollen in marine surface sediments was investigated based on a transect of 12 marine surface sediment samples retrieved from north (29.12AAAAAAAdegreeS) to south (32.50AAAAAAAdegreeS) of the Namaqualand mudbelt off western South Africa. The distinct pollen spectra reflect vegetation communities on the adjacent continent with a marked north-south gradient of pollen concentration. The distribution of specific pollen taxa suggests that the Orange River is a major contribution of pollen to the northern mudbelt declining southwards. Whereas the seasonal inputs of pollen from offshore berg winds and local ephemeral Namaqualand rivers have a great contribution to the central mudbelt. In the southern mudbelt, the dominated Fynbos elements indicate a main pollen source from the Fynbos vegetation in the southwestern Cape of South Africa. The approach in the first part of this thesis allows for climate reconstructions of the SRZ and WRZ using specific pollen taxa from a single marine archive. Therefore, in the second part of this thesis, the Holocene vegetation and climate variability in South Africa was reconstructed using pollen and microcharcoal records of two marine core sites GeoB8331 and GeoB8323 from the Namaqualand mudbelt offshore of the west coast of South Africa covering the last 9900 and 2200 years, respectively. Three different climate periods were described with apparently contrasting climate developments between the SRZ and WRZ: during the early Holocene (9900-7800 cal. yr BP), a minimum of grass pollen suggests lower summer rainfall in the SRZ, while relatively wet conditions in the WRZ were indicated by the initial presence of Renosterveld vegetation. During the middle Holocene (7800-2400 cal. yr BP), a maximum in grass pollen suggests an expansion of rather moist savanna/grassland. This is probably associated with higher summer rainfall in the SRZ resulting from increased austral summer insolation. In the WRZ, a decline of Fynbos vegetation accompanied by an expansion of Succulent Karoo vegetation indicate warmer and drier conditions, which possibly suggests a southward shift of the southern westerlies. Comparing the results of the two sites for the last 2200 years show a more stable climate in the WRZ than in the SRZ. In addition, the a Little Ice Agea (LIA) event (ca. 700-200 cal. yr BP) was detected with colder and drier conditions in the SRZ but colder and wetter conditions in the WRZ. To assess the land-sea linkages in this region, in the third part of this thesis, the Holocene palaeoceanographic and palaeoenvironmental changes in the southern Benguela upwelling system was investigated based on the organic-walled dinoflagellate cyst analysis of 12 marine surface sediment samples and gravity core GeoB8331-4 from the Namaqualand mudbelt offshore of the west coast of South Africa. The results were compared with pollen and geochemical records from the same samples. Three main phases were identified with significantly distinct oceanographic conditions during the Holocene: during the early Holocene (9900-8400 cal. yr BP), warm and stratified conditions were indicated by high percentages of autotrophic taxa suggesting reduced upwelling likely due to a northward shift of the southern westerlies. In contrast, during the middle Holocene (8400-3100 cal. yr BP), cool and nutrient-rich waters with active upwelling were indicated by a strong increase in heterotrophic taxa at the expense of autotrophic taxa. This is probably caused by a southward shift of the southern westerlies. During the late Holocene (3100 cal. yr BP to modern), strong river discharge with high nutrient supply between 3100-640 cal. yr BP was implied by high percentages of Brigantedinium spp. and other fluvial-related taxa such as Protoperidinium americanum and Lejeunecysta oliva
Untersuchungen zur Expression ausgewählter Stammzellgene an embryonalen Geweben und Tumoren
Get PDFHMGA2 and miRNAs of C19MC and miR-371-3 are mainly expressed in embryonic tissues. Reexpression of these genes can be found in different types of tumours. The influence of the above mentioned genes on development and growth was investigated in placentas and testicular germ cell tumours, which mimic embryonic development. Invasive growth is a characteristic of placentas and tumours. Therefore, analysis of the underlying regulation processes in placental development might help to understand the induction of invasive behavior in tumours. In this thesis, investigation of spontaneous and induced abortions and of full-term placentas revealed increasing expression of miRNAs of C19MC with the progression of pregnancy. According to literature, this seems to be related to the regulation of invasive growth of trophoblast cells. Particularly the expression level of miRNAs of the miR-371-3 cluster showed strong interindividual differences. This was not caused by the site of the placenta where the sample has been taken from. Additionally, interindividual differences in expression of miR-371a-3p were also observed in serum samples. It remains to be elucidated whether or not they affect processes during prenatal life. Since there were no differences in expression of spontaneous compared to induced abortions, the miRNAs examined do not play an obvious role in miscarriage events. Investigations conducted in this thesis revealed high HMGA2 expression in first trimester placentas followed by a decline to a baseline level which can be observed until birth. High HMGA2 expression correlated with the low oxygen environment in the uterus in early pregnancy which is known to be a requirement for the proliferation of trophoblast cells. Hence, HMGA2 might function as a proliferation factor in this context. No difference in expression of spontaneous compared to induced abortions could be detected. This indicates that HMGA2 has no obvious role in spontaneous abortions. The stem cell factor HMGA2 was mainly detected in stromal cells of placental villi. This is in concordance with the previous finding that stem cell are located in the stroma of placental villi. Another interesting result of this thesis was the finding that in trophoblast cells HMGA2 is located mostly in the cytoplasma. Cytoplasmatic expression might be related to extravillous differentiation of cytotrophoblast as shown for HMGA1. While physiological expression of HMGA2 is mainly restricted to embryonic tissues and stem cells, reexpression can be observed in different types of tumours. Due to the fact that testicular germ cell tumours mimic embryonic tissues, HMGA2 expression was measured in different types of postpubertal testicular germ cell tumours. Tumours comprising of only one subgroup could be distinguished by qRT PCR expression levels. In frequently found mixed tumours, classification via HMGA2 expression is less distinct. By using HMGA2 immunohistochemistry subgroups could be distinguished. To establish HMGA2 in clinical application, the investigation should be extended on a larger sample. HMGA2 staining showed promising results in detecting choriocarcinoma components. Convincing evidence was found for HMGA2 as an appropriate marker for the detection of yolk sac components
Planktonic foraminifera as signal carriers in paleoceanography: from modern biology to proxy application in the western South Atlantic
Get PDFProxies derived from planktonic foraminifera shell chemistry and assemblage composition allowed to assess past changes in surface hydrography. However, the usefulness of these planktonic foraminifera proxies relies on the understanding of their biology and species-specific environmental preferences. Despite the importance of these evaluations regarding foraminiferal biology, informations about the species reproductive cycle, calcification depth and seasonal fluxes still not well constrained. Therefore, this thesis focuses on the assessment of planktonic foraminiferal biology (e.g. reproduction and calcification depth) and on paleoceanographic application of proxies derived from these organisms in marine archives located at the western South Atlantic, which is a key region due to the presence of boundary currents that transport heat to high latitudes